Low Cost Turbidimeter

AguaClara needs a reliable and simple method for candidate communities to monitor the turbidity of their water supply. Portable turbidimeters cost $400 or more and thus are too expensive to provide to a large number of candidate communities. The goals of providing candidate communities with turbidimeters is to determine the source water turbidity range and hence the type of water treatment that will be required. For example, if the source water turbidity never exceeds 10 NTU, then it may not be necessary to provide flocculation and sedimentation. The turbidimeter should be very inexpensive (less than $20). It should have an error of less than 50%. One possible approach is to use a Jackson style turbidimeter (a long tube that you fill with water until you can't see the candle below the end of the tube). Instead of a candle you could use a waterproof LED in the bottom of a PVC pipe.

See Caroline for an example of turbidity tube that uses a Secchi disk. This method will be highly dependent on ambient lighting.

See The Turbidity Tube:Simple and Accurate Measurement of Turbidity in the Field for some previous research in this area.

Waterproof LEDs are availabe at low cost.

There are two operating modes for the turbidity tubes. Either they can be slowly filled until the light (or secchi disk) disappears or the tube is filled and then the light source can be submerged until it disappears. This later technique is simpler and makes it possible to repeat the measurement easily.

Fabrication Improvements for LFOM, Inlet Manifolds, Plate Settlers, Floc Baffles

Each of these units requires creating large diameter holes in PVC pipe or in plastic sheets. The team in Honduras currently uses a hole saw to create these holes. The hole saw creates a rough hole and when the drilling operation is over the "hole" is inside the hole saw and must be removed. The entire process is time consuming. We need a better way to create these holes. The goal is to come up with improved methods of drill holes that can be tested perhaps even at the Marcala plant that is being constructed right now.
Plate settler spacing may be reduced to 1 cm or even 0.5 cm in the near future. In any case we would like to be able to build plate settler modules with reduced spacing to test their effectiveness in a full scale plant (perhaps at Cuatro Comunidades). We need a method to fabricate plate settler modules with very small spacings between plates. It may be possible to use the same fabrication technique as we are using currently or there may be an easier method.
The Inlet Manifold "centipede" design to reduce horizontal velocities in the bottom of the sed tank needs an improved construction technique. Creating a large contact surface area between the 2 inch PVC pipe and the manifold pipe is necessary for a strong bond. In Agalteca we created a large contact area by heating the 2 inch pipes over a wood fire and then while the plastic is soft molding it to the manifold pipe. This suggests that a viable construction technique would be to cut a large hold in the 2 inch pipe using a hole saw, heat the 2 inch pipe to soften it, mold the 2 inch pipe to the inlet manifold, and then glue the 2 inch pipe to the manifold. Experiment with this fabrication technique and develop improvements.

Trash racks for the entrance tank

The new entrance tank that is being designed by the design team will have a place for trash racks. We need a design for these trash racks that can be easily fabricated. The trash racks should ensure that all debris larger than the openings in the linear flow orifice meter are removed. The head loss through the clean trash rack should also be negligible.

Plant flow rate regulation

We need a method for the operator to regulate the flow through the plant that does not close the valve on the transmission line. This is especially important during high turbidity events. The goal is to keep water flowing through the transmission line even if the plant needs to be shut down so that grit doesn't accumulate in the transmission line and so that it is possible to monitor the turbidity coming from the source. That way the operator will know when it is appropriate to put the plant back on line.
The plant flow rate could be controlled by having an adjustable elevation exit weir (to the drain channel). This should be relatively intuitive for the operator because they already know that the water level in the entrance tank is related to the flow through the plant.
How can we create a weir that can have its height easily adjusted over the entire range of the LFOM (20 cm)?

One possibility is to use a reducing flexible coupling. This coupling would connect a smaller pipe that serves as the drain to a larger diameter pipe that serves as the weir. The coupling would slide over the smaller diameter pipe to be adjustable. This might work, but there are probably better approaches.

Settled (or filtered) water manual pump

Currently the operator needs to fill the chemical stock tanks using a bucket. We need a method that is easier for the operator to fill the stock tanks.
Design a manual pump and plumbing system that can be used to fill the chemical stock tanks. One option for the pump is to use a marble to create a check valve and use a PVC pipe and gasket inside another PVC pipe to create a piston and cylinder. There are many examples including construction details on youtube (http://youtu.be/MwGVH1ADMDs). Determine the design constraints and then build a prototype to test constructability and ease of operation. Consult with the team in Honduras and with their feedback add the pump and plant plumbing additions to the design tool. The plumbing system might include a pipeline from the settled water channel to a "well" below the stock tanks that the manual pump would connect to.

Coagulant concentrations and stock mixing

Experiment with creating a 500 g/L alum stock concentration to see if there are any problems with solubility or high viscosity.
Determine the acceptable range of stock concentrations for poly aluminum chloride (PACl).
Experiment with methods that an operator could use to create stock solutions that minimize how much stirring is required. For example, would it be possible to pump the settled water into a mesh basket holding the alum (or PACl) so that the coagulant would dissolve before dripping into the stock tank?
Design a simple stirrer system that can be added to a 55 gallon drum or to a Rotoplast tank. For an example see the stirrer system that is used at Marcala. Assess what is required to dissolve any granular material on the bottom of the tank and what is required to blend the entire solution. Build a prototype, test it, and then add it to the design tool.

Challenges High Flow Chemical Dose Controller Spring 2011

The High Flow Dose Controller aims to provide AguaClara plants with a simple dose controller  that requires minimal input and oversight from the plant operator.  In keeping with AguaClara standards, this dose controller will not require the use of electricity, will be simple to understand and operate and will be constructed from robust components.  Additionally, the relationship between the driving head and flow rates within the dose controller must match the relationship between plant flow rates and water elevation in the entrance tank. The mechanism for metering flow in both the dose controller and the plant must therefore be the same and will be evaluated as part of the new dose controller design.  The High Flow Dose Controller will be designed for  flow rates where the Linear Dose Controller is unable to meet flow demands.